#print("hello world")

from math import sqrt as sqrt
def area():
    a=float(input("a:"))
    b=float(input("b:"))
    c=float(input("c:"))
    if a+b>c and a+c>b and b+c>a:
        d=(a+b+c)/2
        s=sqrt(d*(d-a)*(d-b)*(d-c))
        print(f"面积:{s:.2f}")
    else:
        print("wrong")
area()
